This invention relates to the curing of polysiloxane (silicone) compositions, which are particularly well suited for application as electronic potting compounds, and coatings.
Potting materials, regardless of the chemistry, are used for sealing electrical connectors, temperature probes and sensors in applications throughout the aerospace, defense, electronic, electrical, industrial, and marine industries. Potting compounds and encapsulants provide vibration and shock resistance, corrosion protection and thermal stress protection to sensitive electronic components. These materials range in character from very hard, rigid thermoset epoxies to soft, “gel-like” silicones. U.S. Pat. Nos. 3,933,712 and 4,374,967 give a more extensive description of silicone gels. Due to their superior moisture resistance, thermal stability, cold temperature flexibility and dielectric strength, silicone based products are used extensively in the electronics industry as potting and encapsulating compounds on integrated circuit boards.
Conformal coatings, which are similar in composition to the potting and encapsulating materials, protect integrated circuit boards, and other system components from damage which may happen during fabrication, shipping and handling. Currently, silicone RTV's (room temperature vulcanization) provide satisfactory coatings. These materials, which cure when exposed to atmospheric moisture, are commercially available and well known in the art. Further information and examples of these systems are found with reference to the following U.S. Pat. Nos. 4,017,495; 3,816,184 and 3,592,795. However, moisture-cured RTV's are generally slow, requiring at best several hours, but often several days to reach full strength. U.S. Pat. No. 4,087,585 describes a two-component system which yields faster cure times if elevated temperatures are provided. Two-component products frequently require specialized mixing equipment, and extraordinary cure conditions. This adds a level of complexity to the fabrication process, which generally increases the cost of production.
A dual-cure silicone composition is provided having a first polysiloxane component and a second polysiloxane component, wherein the first polysiloxane component is selected from the group consisting of: a) polyorganosiloxanes having terminal mercapto and alkoxy functionality, and b) dimethylmercapto terminated polydimethylsiloxanes; and wherein the second polysiloxane component is selected from the group consisting of: a) polyorganosiloxanes having terminal vinyl and alkoxy functionality, b) vinylmethylsiloxane copolymers that are trimethyl terminated and have vinyl functionality pendent to the polymer backbone, and c) dimethylvinyl terminated polydimethylsiloxanes.